Primary

chromium

productionChromium

oresCrocoite

(PbCrO4)Chromite(FeCr2O4;MgCr2O4)monoclinic

crystal

systemisometric

crystal

systemIntroduction

of

Chromium

oresCrocoiteCrocoiteisamineralconsistingofleadchromate,PbCrO4,andcrystallizingithemonocliniccrystalsystem.Itiscommonlyfoundaslarge,well-developedprismaticcrystals,althoughinmanycasesarepoorlyterminated.OnexposuretoUVlightsomeofthetranslucencyandbrilliancyislost.ChromiteChromiteistheonlyvaluableoreofchromiumtoproductchromium（III）oxide.Chromiteisanoxidemineralcomposedofchromium,ironandoxygen(FeCr2O4).Itisadarkgraytoblackincolorwithametallictosubmetallicluandahighspecificgravity.Itoccursinbasicandultrabasicigneousrocksaninthemetamorphicandsedimentaryrocksthatareproducedwhenchromite-bearingrocksarealteredbyheatorweathering.Identification

of

Chromate

MineralIndustrial

production

of

Cr2O3（solid-phase

synthesis）Intheindustryfieldsthegeneralproductionmethodissolid-phasereactionbycalciningCrO3.Undertheconditionsof700℃and90minutes,when2%~3%ofthecombustiblepowderandtheadequatewaterwereadded,itshowedthatthesizeofCr2O3powderwasabout200nm.以鉻酸酐熱分解制備Cr2O3工藝為基礎,在可燃性粉末質量分數2%~3%、適量水,溫度為700℃,時間為90min的條件下,可得到平均粒徑為200nm,分散性良好的Cr2O3微粒。Solid-phase

Reaction

Process(the

reaction

principles)Calcining

CrO3:The

overall

reaction

:4CrO3

2Cr2O3+3O2Solid-phase

Synthesis

Process（preparation）CrO3

HCrO4remove

inflammable

powder

Cr2O3Industrial

production

of

Cr2O3（calcining

chromium

hydroxide）Thesodiumchromatesolutionwasaddedsulfurtoreducehexavalentchromiumtotrivalentchromium，thenformingtheprecipitationofchromiumhydroxide.atlastgeneratingchromiumoxidebycalciningchromiumhydroxide.氫氧化鉻法:將鉻酸鈉溶液加入硫磺還原鉻酸鈉溶液，使鉻從六價還原成三價從而形成氫氧化鉻沉淀，然后煅燒脫水變成氧化鉻。反應式:4Na2CrO4+6S+7H2O=4Cr(OH)3↓+3Na2S2O3+2NaOH2Cr(OH)3=Cr2O3+3H2OCalcining

chromium

hydroxide（preparation）硫磺塊破碎機球磨機水或上液層反應罐鉻酸鈉溶液蒸汽水管式過濾器上層液制硫代硫酸或碳酸鈉洗滌罐硫酸離心分離機煅燒水破碎氧化鉻laboratory

preparation

of

Cr2O3Experimentalprinciple:HydrothermaltechniquebythereactionsystemofCrO3andHCHOinaqueoussolutionExperimentalprocedure:5gCrO3and3.5mlHCHOaqueoussolutionwereaddedintoa200mlTeflon-linedcylindricalbombpreviouslyfilledwith120gdeionizedwater,andmagneticallystirredforseveralminutesuntiltheybecameahomogeneoussolution.Thenthesealedbombwasheatedat170℃for1hinanoven.Afterthat,itwascooledtoroomtemperatureandthesolutionwasfiltered.Thefiltercakewaswashedfor3times.Thenthecakewasdriedat100℃for5h.Theobtainedparticleswereblack,withsizeinthegradeofμmtomm.laboratory

preparation

of

Cr2O3The

possible

mechanism

was

concluded

as

follows:laboratory

preparation

of

Cr2O3Prospect:Thehydrothermalsynthesisneedsnosurfactantorstirrer.Andhighercalcinationtemperatureandhighertotalconcentrationcouldresultinlargeraveragepar-ticlesi